Notch pathway signaling is involved in numerous cellular processes, including cell fate determination, differentiation, proliferation, apoptosis, migration and angiogenesis. In mammals, there are four Notch proteins (sometimes called “Notch receptors”), designated Notch1-Notch4. All four Notch proteins have a similar domain structure, which includes an extracellular domain, a negative regulatory region (NRR), a single-pass transmembrane domain, and an intracellular domain. The extracellular domain contains a series of EGF-like repeats that are involved in ligand binding. During maturation, the Notch polypeptide is cleaved by a furin-like protease. This cleavage divides the Notch protein into two subunits that are held together by noncovalent interactions of the NRR. In the absence of ligand binding, the NRR domain functions to keep the Notch protein in a protease-resistant conformation. The intracellular domain is a transcription factor called Notch intracellular domain (NICD), which is released upon proteolytic cleavage by gamma secretase, in response to binding of the Notch protein by a ligand. In mammals, the Notch ligands are Delta-like (e.g., DLL1 and DLL4) and Jagged (also referred to as Jag, e.g., Jag1 and Jag2). When the NICD is released, it travels to the nucleus, where it activates transcription of the Notch-responsive genes, HES1, HES5, NRARP, Deltex1 and c-MYC. For reviews of Notch-related biology, see, e.g., Bray, 2006, NATURE REVIEWS 7:678-689; Kopan et al., 2009, CELL 137:216-233.
While Notch proteins play crucial roles in normal development, dysregulation of the Notch proteins is associated with various types of cancer, including T-cell acute lymphatic leukemia/lymphoma (T-All), breast cancer, colon cancer, ovarian cancer and lung cancer. See, e.g., Miele et al., 2006, CURRENT CANCER DRUG TARGETS 6:313-323. Accordingly, one therapeutic approach for the treatment of cancer is inhibition of Notch pathway signaling. Inhibition of Notch pathway signaling has been achieved using monoclonal antibodies (Wu et al., 2010, NATURE 464:1052-1057; Aste-Amézaga et al., 2010, PLOS ONE 5:1-13 e9094).
Naturally-occurring antibodies are multimeric proteins that contain four polypeptide chains (FIG. 1). Two of the polypeptide chains are called immunoglobulin heavy chains (H chains), and two of the polypeptide chains are called immunoglobulin light chains (L chains). The immunoglobulin heavy and light chains are connected by an interchain disulfide bond. The immunoglobulin heavy chains are connected by interchain disulfide bonds. A light chain consists of one variable region (VL in FIG. 1) and one constant region (CL in FIG. 1). The heavy chain consists of one variable region (VH in FIG. 1) and at least three constant regions (CH1, CH2 and CH3 in FIG. 1). The variable regions determine the specificity of the antibody.
Each variable region contains three hypervariable regions known as complementarity determining regions (CDRs) flanked by four relatively conserved regions known as framework regions (FRs). The three CDRs, referred to as CDR1, CDR2, and CDR3, contribute to the antibody binding specificity. Naturally occurring antibodies have been used as starting material for engineered antibodies, such as chimeric antibodies and humanized antibodies.
There is a need for improved antibodies that neutralize the biological activity of human Notch3 and that can be used as therapeutic agents to treat human patients.